1. Field of the Invention
This invention pertains to a method for generating high resolution surface topology maps, and more particularly, to a method for generating high resolution surface topology maps using surface profiling data combined with data collected from a land surveying instrument, such as either a total station or a Global Positioning System with Real Time Kinemetic (RTK) surveying device, such as a Carrier-Phase Enhancement GPS System (CPGPS) using a single reference station or a Virtual Reference Station (VRS) using a group of networked reference stations.
2. Description of Related Art
Land surveying instruments are used to generate three-dimensional topography maps of surfaces at grade for use in civil engineering and construction projects. Currently two types of surveying instrument systems are in common use, total stations and radio transmitted Real Time Kinematic (“RTK”) correction devices. In various configurations, both types of surveying instruments may be used with GPS data.
A total station is an optical instrument used in modern surveying. A total station system includes a base station equipped with a computer, a laser, and an optical receiver. The total station is designed to work in cooperation with a prism, which is moved to various points on the surface to be mapped. During operation, the prism is moved from point to point within the area to be surveyed. At each point, the laser transmits a signal from the base station to the prism, which reflects the signal back to the optical receiver at the base station. The computer at the base station then calculates the X, Y and Z coordinate of the location of the prism. The X and Y coordinates are calculated by the round-trip travel time of the laser. The Z coordinate is determined by the angle of the return laser signal. By calculating the X, Y and Z coordinate of many surface sample points, an accurate topological map of the area to be surveyed may be generated. One disadvantage of conventional total stations is that they require a line of site between the base station and the prism at the point to be surveyed. Without a line of sight, the aforementioned angle and distances cannot be determined. Any resulting surface topology map will therefore be incomplete. To address this issue, more advanced total station devices use GPS information instead of line of sight measurements. The disadvantage of GPS information, however, is generally inferior accuracy in the vertical or Z direction.
Real Time Kinematic (“RTK”) surveying devices rely on Global Positioning System (“GPS”) technology to improve the accuracy of sampled survey data points. With RTK systems, a static base GPS unit is used in cooperation with a roving GPS unit. The static base GPS unit accurately measure its position relative to one or more GPS satellites or a Virtual Reference System (VRS), which is a group of networked base stations located in the general vicinity of the area to be surveyed. In either case, the static base unit measures atmospheric and other disturbances that may cause positional errors. Once the static base station locks-in and accurately determines its position, it transmits a corrections factor signal to the roving GPS unit, which compensates for any measured atmospheric or positional errors.
During the surveying process, the roving GPS unit moves across the surface to be mapped, sampling and measuring the X, Y and Z coordinate of multiple points within the survey area. The correction factor signal from the static base GPS unit is then applied to the measured X, Y and Z coordinate of each sample point, correcting for any inaccuracies due to atmospheric and other disturbances. The compensated X, Y and Z coordinate for the sampled points are therefore more accurate than if the correction factor was not applied. Again, by computing the X, Y and Z coordinate for multiple sample points across the area to be surveyed, an accurate surface topology map may be generated. A disadvantage of both GPS and VRS systems is their inability to function in areas of overhead cover (wooded areas, urban areas, inside buildings, etc.), where clear access to the GPS satellite is either partially or fully blocked.
In the road construction industry, inertial profiling systems are increasingly popular devices used for quality assurance and quality control purposes. The most common use of inertial profilers is to test the surface ride quality or “smoothness” of the top layer of asphalt or concrete pavement on road surfacing construction projects. Transportation agencies also commonly use inertial profiling systems for pavement management and maintenance applications. Roads are periodically analyzed for condition assessment and for making decisions with regard to rehabilitating or resurfacing of the roadway.
The profile of a surface generated by an inertial profiling system is a relative profile, not an absolute or true profile. Inertial profilers generate only a two-dimensional surface profile along a longitudinal surface in the X and Y dimensions, along the path traveled by the profiler. Inertial profiling systems, however, do not generate a true profile since they do not record absolute elevation readings in the Z dimension, as do RTK or total stations surveying instruments. Thus while an inertial profiling system can accurately detect the changes in the surface profile contour between points A and B on a given road surface, they cannot detect the absolute change in elevation from point A to point B.
Inertial profiling systems are typically vehicle mounted devices generally consisting of laser sensors for measuring vertical displacement from a fixed point on the vehicle to the ground underneath, accelerometer sensors to measure the vertical acceleration of the vehicle, and a distance measurement interface to record the vehicle's longitudinal movement in the direction of travel. Commercially available inertial profiling systems typically have a very high degree of resolution. Many commercially available profilers are capable of acquiring valid samples at one-inch (25 mm) increments along the traveled surface and can detect changes in surface profile conditions on the order of 0.001 inches. Inertial profiling systems can collect data samples at one inch (25 mm) at speeds up to 70 mile per hour (112 kilometers per hour). In contrast, both total stations and RTK surveying devices have a lower resolution than inertial profiling systems if only relative profile data is considered, but those devices have a much higher resolution in capturing the Z dimension necessary to generate an absolute or true profile. While the resolution of both total stations and RTK surveying devices is sufficient for some applications, the resolution of these devices alone is not adequate or optimal for other applications, such as high tolerance surface design, construction project progress monitoring, or precision machine control, where a highly accurate and more resolute surface topology is desirable.
For the above reasons, a method for generating high-resolution surface topology measurements using surface profiling data combined with data collected from a surveying instrument, such as either a total station or a Real Time Kinematic (RTK) surveying device, including either a total station RTK surveying device used with either GPS or VRS, is needed.